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How to Replace Words in Strings with Dictionary Values in Pytho

This guide explains how to replace specific words in a Python string with corresponding values from a dictionary. This is a common task in text processing, template rendering, and data manipulation. We'll cover both case-sensitive and case-insensitive replacements, using straightforward loops and the more powerful re.sub() function for regular expression-based substitutions.

Case-Sensitive Replacement with a for Loop​

The most basic approach is to iterate through the dictionary's key-value pairs and use str.replace():

my_str = 'site | name'

my_dict = {
    'site': 'tutorialreference.com',
    'name': 'tom'
}

for key, value in my_dict.items():
    my_str = my_str.replace(key, value)

print(my_str)  # Output: tutorialreference.com | tom
  • my_dict.items(): This method returns a view object that displays a list of a dictionary's key-value tuple pairs.
  • The for loop iterates over the dictionary's key-value pairs.
  • my_str.replace(key, value): This replaces all occurrences of the key (in the string) with the corresponding value. The replace() method does not modify the original string; it returns a new string with the replacements made. That's why we reassign the result back to my_str.
note

This approach performs a case-sensitive replacement. "site" will be replaced, but "Site" or "SITE" will not.

Case-Insensitive Replacement with a for Loop​

For case-insensitive replacement using a loop, convert both the key and the string being searched to lowercase (or uppercase) before calling replace():

my_str = 'site | name'

my_dict = {
    'SITE': 'TUTORIALREFERENCE.COM',
    'NAME': 'TOM'
}

for key, value in my_dict.items():
    my_str = my_str.replace(key.lower(), value.lower())

print(my_str) # Output: tutorialreference.com | tom
  • key.lower() and my_str.lower(): Convert both to lowercase before comparison. This performs a case-insensitive replacement.

Case-Sensitive Replacement with re.sub()**​

You can also use regular expressions with re.sub() method for performing replacements:

import re

my_str = 'site | name'
my_dict = {
 'site': 'tutorialreference.com',
 'name': 'tom'
}

for key, value in my_dict.items():
  my_str = re.sub(key, value, my_str)

print(my_str) # Output: tutorialreference.com | tom

Case-Insensitive Replacement with re.sub()​

For more powerful and flexible replacements, especially when dealing with case-insensitivity or word boundaries, use the re.sub() function from the re (regular expression) module:

import re

my_str = 'site | name'
my_dict = {
    'SITE': 'TUTORIALREFERENCE.COM',
    'NAME': 'TOM'
}

for key, value in my_dict.items():
    my_str = re.sub(key, value.lower(), my_str, flags=re.IGNORECASE) #Using re.sub

print(my_str) # Output: tutorialreference.com | tom
  • re.sub(pattern, repl, string, count=0, flags=0): This function replaces occurrences of a pattern in a string with a repl (replacement).
    • key: The dictionary key (which we'll treat as the "word" to replace).
    • value.lower(): The replacement value (converted to lowercase in the example for consistency)
    • my_str: The string in which we're making replacements.
    • flags=re.IGNORECASE: This makes the search and replace case-insensitive.
  • The for loop iterates through the key-value pairs, substituting the values.

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